Method of producing a dehumidifying element

Details Method of producing a dehumidifying element Method of producing a dehumidifying element

1999-10-12

2001-07-24

Beck, Shrive (Department: 1762)

Coating processes

With post-treatment of coating or coating material

Heating or drying

C427S398100, C427S434200, C427S439000, C162S111000, C162S112000, C162S135000, C162S181700

Reexamination Certificate

active

06265030

ABSTRACT:

The present invention relates to the dehumidification of air with the aid of a dehumidifying element that comprises a fibre matrix which has been impregnated with waterglass. More specifically, the invention relates to a method of producing dehumidification elements.
TECHNICAL BACKGROUND
Air is normally dehumidified with the aid of a dehumidifying element that can be fabricated by joining together a flat and a pleated fibre material that has moisture absorbing properties to form a laminate which is rolled into the form of a rotor or stacked in block form. A laminate of this nature is shown in FIG.
3
. The dehumidifying element can be said to resemble corrugated paperboard that has been rolled up to form a rotor, or corrugated board that has been cut into lengths and the lengths stacked together to form a block. This element includes a structure that has many mutually parallel passageways. The pleats are normally from 1.5 to 3 mm in height and the passageways have a length of from 50 to 400 mm. A sector of one such rotor is shown in FIG.
4
.
The initial roll or block is sawn and ground to form a rotor, which is often provided with a hub, spokes and/or cowling. The rotor forms the “heart” of an air dehumidifier, in which a fan or blower drives the air through the numerous rotor passageways. Because the walls of the passageways include a moisture absorbent, the air will be dry subsequent to passing through the rotor. A small heated air flow passes through a minor sector in the rotor and expels the moisture therefrom. Dry air is produced continuously, by continually rotating the rotor between the sections containing air to be dehumidified and sections through which heated air passes. The moisture extracted is carried away with the heated air flow in a separate passage system. This principle is illustrated in FIG.
5
.
SE,B,460 705 teaches a method of producing a dehumidifying element in which paper comprised of ceramic fibres is impregnated with a waterglass solution either prior to or subsequent to lamination, and in which the paper is heated after being impregnated and dried to form a hydrated waterglass having a water content of 3-20%. The resultant matrix is then submerged in acid, so as to form silica-hydrogel.
SE,B,460 021 teaches a humidifying element that consists of a laminate which comprises a sheet of ceramic fibres that is corrugated on one side and has a paper thickness of 0.18-0.25 mm, a wave length of 2.5-4.2 mm and a wave height of 1.5-2.3 mm. This laminate is impregnated with an active silicon dioxide-aluminum oxide-aerogel that comprises 97-85% silicon dioxide and 3-15% aluminum oxide. The element is produced by dipping ceramic paper into an aqueous solution of waterglass, and then dried. The element is then dipped into an aqueous solution of aluminum sulphate and again dried.
SE,B,462 671 describes a method of producing a dehumidifying element in which a laminate consisting of an undulating sheet and a flat sheet is impregnated with an aqueous solution of waterglass, followed by drying the laminate and heating the same to a water content of 5-45%, whereafter the laminate is dipped in an aqueous metal salt solution and finally dried and heated.
SE,B,469 976 describes a method of producing dehumidifying elements in which paper webs that include a shapeable material, such as glass fibre or cellulose, are drenched with concentrated waterglass solution and dried to a dry solids content of about 45-65% with respect to the waterglass, and then corrugated. The corrugated laminate is then dried to a dry solids content of about 60-95%.
EP,B,0,642,384 describes a method of treating dehumidifying elements with the purpose of influencing the pore size of the silica gel. This is achieved by treating the dehumidifying elements with acid, base and a stabilising solution that contains salts of zinc, aluminium and phosphate. It is also stated in this prior application that waterglass is applied to the paper and that the waterglass is then dried. All of the aforesaid documents describe an impregnating stage followed by a drying stage in conjunction with the preparation of dehumidifying elements that comprise a silica gel matrix.
Drying stages are energy consuming and therewith add to production costs. Furthermore, sufficient quantities of waterglass cannot be readily applied when the solution has the low concentration required by known technology. Consequently, the dehumidifying elements produced will have a limited amount of silica gel and the capacity of said elements will not be optimal. There is therefore a need for improved methods that lower production costs and raise the performance and quality of the end product.
SUMMARY OF THE INVENTION
It has been found that the drying stage that follows immersion of paper into the waterglass solution can be eliminated totally and that the amount of silica gel matrix applied can be increased at the same time, by applying a method that includes the steps of
a) providing a paper sheet, such as a sheet of facing paper and/or undulated paper;
b) submerging the paper in a highly concentrated waterglass solution at a temperature in the range of 45-95° C.; and
c) cooling the submerged paper with air at a temperature not higher than 35° C. and preferably at 25° C. at the highest.
Definitions
The term “waterglass” as used in this document refers to aqueous solutions of sodium silicate (“soda waterglass”) or potassium silicate. Sodium waterglass and potassium silicate are often written as (Na
2
O)
m
(SiO
2
)
n
and (K
2
O)
m
(SiO
2
)
n
respectively, from which it will be seen that the mole ratio between the two oxides (n/m) can vary. In the case of the present invention, soda waterglass with n/m within the range of 3.3 to 3.4 is preferred, and waterglass with n/m from 3.2 to 3.4 is particularly preferred.
The expression “highly concentrated waterglass” as used in this document refers to waterglass that has a lower viscosity limit of at least 350 mPa·s at 45° C. The upper viscosity limit is 800 mPa·s at 95° C. The viscosity of highly concentrated waterglass at room temperature is so high as to make it extremely difficult to submerge paper in the waterglass and for the waterglass to wet the paper at this temperature. According to known technology, a typically concentrated waterglass at 20° C. has a viscosity of up to 200 mPa·s. Highly concentrate waterglass, on the other hand, has a much greater viscosity at 20° C. and in its least concentrated form can be likened to cold syrup or treacle.
The term “paper” as used in this document refers to sheets produced from organic fibres, such as cellulose, or inorganic fibres, such as ceramic fibres, glass fibres, slag fibres, carbon fibres and mineral fibres, and mixtures thereof. Inorganic fibres are preferred. It is also preferred to use glass fibres and/or mineral fibres in mixture with up to 20% cellulose fibres or synthetic fibres. The paper will typically have a thickness of 0.1-0.3 mm. The wave height of the undulating paper will typically be from 1-5 mm and the wave length typically from 1.5-7 mm. The paper will have a typical weight per unit area of 20-50 g/m
2
.
DETAILED DESCRIPTION OF THE INVENTION
As mentioned earlier, the invention relates to a method of producing dehumidifying elements that comprise a paper matrix that has been impregnated with waterglass which is later converted to silica gel. Instead of using concentrated waterglass as a silica gel starting material, there is used highly concentrated waterglass. This waterglass is so highly viscous as to render it practically impossible to impregnate paper at room temperature. However, the highly concentrated waterglass becomes fluid at temperatures of from 45-95° C. and functions in the manner of concentrated waterglass. The paper that is to be impregnated is thus immersed into hot highly concentrated waterglass and then cooled with air having a temperature of 35° C. at the highest, preferably at 25° C. at the highest. It is not necessary to dry the paper. The cooled, impregnated paper also has good adhesive properties and can be easily j

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